The intercalated disc of mammalian myocardium contains nexuses or gap junctions (A type). Do these junctions show voltage dependent behavior? This study proposes to use an experimental model system, the septate axon of the earthworm, to voltage clamp junctional membranes under varied conditions. This study proposes to distinguish voltage - dependent junctional membrane conductance changes from pH dependent changes. The homogeneity of junctional membrane function will also be tested by measuring junctional conductance first in the absence of large probes and then with them present. Will the probes decrease junctional conductance? If so, to what extent? The methods given in this proposal will answer these questions. The double voltage clamp is a useful tool in maintaining steady transjunctional potentials while uncoupling cells and will allow uncoupling to be studied without any changes in transjunctional voltage.